Generally, a motor vehicle powershift transmission includes a number of gear elements coupling the input and output shafts, and a related number of clutches which are selectively engageable to activate gear elements for establishing a desired speed ratio between the input and output shafts. The clutch may be of the band or disk type.
For example, the input shaft may be connected to the engine through a fluid coupling, such as a torque converter, and the output shaft is connected directly to the vehicle drive. Shifting from one gear ratio to another involves releasing or disengaging the off-going clutches associated with the current gear ratio and applying or engaging the on-coming clutches associated with the desired gear ratio.
Shifts performed in the above manner are termed clutch-to-clutch shifts and require precise timing in order to achieve high quality shifting. However, if a shift to one gear ratio is suddenly interrupted with a shift to another gear ratio, the timing or sequence of engagement and disengagement of the clutches becomes even more critical to achieve high quality shifting.